The present invention generally relates to methods and apparatuses for controlling source chemical delivery by a carrier gas, and more specifically relates to a method and apparatus for controlling source chemical delivery by a carrier gas where the delivery is controlled based on detected light absorption properties of the flow.
Chemical applications exits where a source chemical is delivered using a carrier gas. Specifically, the carrier gas is bubbled up through the source chemical (a liquid) contained in a vessel, and is delivered to, for example, a processing chamber. When the carrier gas “bubbles” through the source chemical to the top of the vessel, molecules of the source chemical attach to the carrier gas and is carried to the processing chamber. One such application is the processing of wafers (i.e., in the manufacture of semiconductor devices). In such an application, a typical source chemical may include TEOS (tetraethylorthosilicate), TMB (trimethylborate), TEPO (triethyiphosphate), TMP (trimethylphosphite), TMPO (triethyiphosphate) or POCL (phosphorusoxychloride) (and many others), and a typical carrier gas may include He (Helium) or N2 (Nitrogen).
The amount of source chemical carried into the processing chamber is not typically constant, and changes based on several different factors or parameters, such as the amount of source chemical contained in the vessel, the concentration of dopant in the source chemical, the temperature of the vessel, the temperature of the carrier gas, pressure of the carrier gas, flow of the carrier gas, etc. As the amount of source chemical attached to the carrier gas changes, the process in the processing chamber also changes.
Presently, the delivery of source chemical using a carrier gas is controlled based on indirect measurements of the many factors or parameters which affect the delivery. However, inputs can and do change, and the amount of source chemical delivered using the carrier gas changes despite the desire to have such delivery be constant and be directly and predictably controlled. In the case of wafer processing, such undesirable variance in the amount of source chemical delivered results in undesired changes in the thicknesses of films being deposited on the wafer. This is evidenced in the outputs of the process, and is a direct result of the inconsistent and unreliable control of the reactants to the process In other words, direct measurement of the reactant (i.e., the concentration of source chemical being delivered by the carrier gas) is not performed and instead, the delivery of source chemical is controlled through monitoring those parameters which affect the delivery. Such a process provides a method of delivering source chemical which is relatively unpredictable and unreliable.